Classification of Metamorphic Rocks

Dr. Ahmad Redaa

2024-10-14

Introduction

Foliated Metamorphic Rocks

  1. Slate
  2. Phyllite
  3. Schist
  4. Gneiss

Slate

Source: https://openpress.usask.ca

Phyllite

Source: https://openpress.usask.ca

Schist

Source: https://openpress.usask.ca

Gneiss

Source: https://openpress.usask.ca

Non-foliated Metamorphic Rocks

Marble

Source: https://openpress.usask.ca

Quartzite

Source: https://openpress.usask.ca

Hornfels

Source: https://openpress.usask.ca

Metamorphic Rock Names

Classification based on protolith composition (original rock)

Pelites

Psammites

Calcareous Rocks

Quartzo-Feldspathic Rocks

Mafic Rocks

Ultramafic Rocks

Summary Table

Classification Protolith Composition Common Minerals Examples (Before) Examples (After)
Pelites Mudstone, shale High aluminum Mica, garnet, kyanite Shale, mudstone Slate, schist, gneiss
Psammites Sandstone High silica (quartz, feldspar) Quartz, feldspar Sandstone Quartzite, meta-sandstone
Calcareous Rocks Limestone, dolostone High calcium carbonate Calcite, dolomite, diopside Limestone, dolostone Marble, calc-silicate rock
Quartzo-Feldspathic Rocks Granite, arkosic sandstone High quartz and feldspar Quartz, feldspar Granite, arkose Gneiss, granulite
Mafic Rocks Basalt, gabbro Moderate silica, high Fe, Mg Amphibole, pyroxene, plagioclase Basalt, gabbro Amphibolite, granulite
Ultramafic Rocks Peridotite Very low silica, high Mg, Fe Olivine, serpentine, talc Peridotite

Another Genetic Classification

Para- Metamorphic Rocks

Ortho- Metamorphic Rocks